Band inserted on the left travels to the
right. Snapshots in time are shown as the band travels around the bends. Note the complementary turns do not completely undo the skew of previous turn. The band spreading grows quadratically after complementary turns, limiting the system's resolving power.
Double-tee injector shown in (a), cross
injector shown in (b). Band is injected towards the right in both cases. Both injectors create unique band shapes which have been modeled
and implemented in Verilog-A for circuit simulation.

Project:
The synthesis of complex microfluidic lab on a chip devices can be a
difficult and time consuming process because of its combination of
different types of physics and high level of component interaction. To
create a typical lab on a chip device you must design each section
independently (mixer, reactor, injector, separator) and iterate on the
combined system design. This work attempts to make this process faster
and more accurate with complete system circuit simulation using accurate
compact models of each component of the microfluidic chip. In
particular, this research explores the low-diffusion physics of
serpentine separation channels and component based multi-regime injector
models. These models are combined with models of the other on-chip
components to create a Verilog-A circuit simulation environment. The
circuit simulation provides an intuitive methodology for designing and
validating devices, shortening the time to fabrication.

Selected Highlights:
If a system is to separate several species with very similar mobilities,
a long separation length will be required. To achieve this long length
in centimeter size chips, it is common to bend the channels in a
serpentine manner to more efficiently use the chip area. If the
separation species have a low diffusivity, the system will be subject to
high Peclet dispersion that presents a system stability issue. Figure 1
shows an individual species traveling through one of these serpentine
systems. In these systems, the dispersion creates a spreading of the
band that grows quadratically after each set of complimentary bends in
the channel, making it potentially impossible to sufficiently resolve
the individual species. It is useful to be able to identify systems
that fall into this regime, so models of the band dispersion in the high
Peclet regime were created. Another system component that affects the
species resolving power is the injector. The injector shapes the species into bands for entry into the separation channel, therefore it is the
component that connects all of the upstream components (mixing,
reacting) to the downstream components (separation, detection). Models
have been created for the two most common injector topologies, as shown
in Figure 2. These models have been implemented into Verilog-A. System
circuit simulations have been performed on systems including mixing,
injection, separation, and detection. These simulations take on the
order of seconds to minutes to complete, compared to the days or weeks
of numerical simulation, allowing design iteration to be much more
tractable. System verification with experimental and numerical results
is underway.